04 research methods

What are the three main categories of methods for studying brain functions?

• Visualize: Show brain structure or activity in brain areas (e.g., CT, MRI, fMRI, PET, fNIRS)

• Stimulate: Activate/inactivate brain areas and investigate effects on behaviour/cognition (e.g., TMS, tDCS)

• Measure: Record brain activity and relate it to behaviour/cognition (e.g., EEG, MEG, EMG, EOG, skin conductance, ECG)

What is CT (or CAT) scanning? How does it work? What are its strengths/weaknesses?

• Principle: Uses X-rays to produce images of brain structure

• How it works: Multiple X-ray beams are passed through the head; detectors measure absorption; a computer reconstructs a cross-sectional image

• Strengths:

  • Fast (5–10 min)

  • Good for bony structures

  • Less expensive than MRI

• Weaknesses:

  • Radiation exposure

  • Lower detail in soft tissue

• Comparison with MRI: CT is X-ray based; MRI uses magnetic fields (no radiation). MRI is better for soft tissue (brain, spinal cord); CT better for bone, lung, abdomen.

What is MRI? What is fMRI and what does BOLD measure?

• MRI (Structural):

  • Uses strong magnetic fields and radio waves

  • Hydrogen atoms/protons act like tiny magnets; different tissues (white vs grey matter) produce different signals

  • No radiation exposure, high soft-tissue detail

  • Longer examination time (15–45 min)

• fMRI (Functional):

  • Measures BOLD signal (blood oxygenation level dependent)

  • Active brain areas need more oxygen → deoxyhemoglobin increases → increased blood supply → oxygen concentration changes → MR signal changes

  • Haemodynamic response function: mathematical model describing BOLD signal changes over time after neural activity

  • Shows which brain areas are active during a task (correlational, not causal)

What is PET? What tracers are used? What does it measure?

• Principle: A radioactive chemical (radiopharmaceutical) is injected; organs/tissues absorb it; the PET scan measures levels of radioactivity

• Tracers:

  • FDG (fluorodeoxyglucose): similar to glucose → taken up by active (energy-consuming) cells

  • 18F-DOPA: radioactive analog of L-DOPA → absorbed by cells producing dopamine or serotonin

  • Radio-ligands: bind to neurotransmitters, receptors, transporters, amyloid plaques, etc.

• Use: Visualizes brain activity, receptor distribution, neurotransmitter systems

• Note: PET is invasive (radioactive injection) and has lower spatial resolution than MRI

How does fNIRS work? What are its pros and cons?

• Principle: Near-infrared light is sent through the skull; photons scatter through brain tissue and are differently absorbed by oxygenated (HbO₂) and deoxygenated (Hb) hemoglobin

• "Photon Banana": Light penetrates only ∼2–3 mm into the cortex

• Measures: Changes in HbO₂ and Hb concentration → brain activity

• Pros:

  • Transportable, flexible → can be used in natural environments

  • Good temporal resolution

  • Relatively inexpensive

  • Robust against movement artefacts

• Cons:

  • Low spatial resolution

  • Only cortex can be measured (not deep structures)

What are TMS and tDCS? How do they establish causality?

• Transcranial Magnetic Stimulation (TMS):

  • An electromagnetic coil is placed next to the skull; magnetic fields can turn off/on an area of the cortex

  • Non-invasive

  • Directly tests causal relations between brain (in)activity and behaviour/cognition

  • Used before surgery (e.g., tumor removal) to determine how much tissue can be removed

• Transcranial Direct Current Stimulation (tDCS):

  • Induces a weak electrical field

  • Anodal stimulation: enhances activity of synapses

  • Cathodal stimulation: suppresses activity of synapses

  • Also non-invasive

• Key point: Stimulation methods allow stronger causal inferences than purely correlational imaging methods.

What is EEG? What are ERP components? What are brain oscillations?

• EEG: Records electrical activity of the brain via electrodes on the scalp; amplified and recorded

  • Differentiates spontaneous brain activity from stimulus-evoked activity

  • Electrode placement: 10–20 system

• ERP components (time-locked):

  • N1 (N100): 90–200 ms – orienting response, encoding

  • P2 (P200): 100–250 ms – attentional processes, storage of information

  • N2: N2a/MMN (mismatch negativity), N2b (physical stimulus changes), N2c (classification)

  • P3 (P300): 250–400 ms – cognitive processes, conscious processing

• Oscillations (frequency bands):

  • Delta: sleep

  • Theta: drowsiness, learning, memory

  • Alpha: relaxed awake

  • Beta: mental/physical/psychological activity

  • Gamma: representation and analysis of perceptual objects

• Example: Athletes show larger N2 amplitudes in mental rotation tasks → they process stimuli differently than non-athletes.

What are EMG, EOG, skin conductance, and ECG/BP used to measure?

• EMG (Electromyography):

  • Measures muscle tension – electrical activity generated when muscles contract

  • Somatic nervous system activity

• EOG (Electrooculography):

  • Records eye movements via electrodes above/below and left/right of the eye

  • Indicator of attention, perception, arousal, sleep stage

• Skin conductance:

  • Sweat glands become active in emotional situations → increases electrical conductivity of skin

  • Indicator of emotional thoughts and experiences

• Cardiovascular activity:

  • ECG (Electrocardiogram): electrodes on chest → heart rate

  • Blood pressure

  • Both are indicators of emotional arousal

• Key point: These measure activity of the peripheral nervous system(somatic and autonomic), not directly the brain.

What are lesion methods? What types exist? Why is interpretation difficult?

• Definition: A part of the brain is damaged, destroyed, or inactivated

• Types:

  1. Aspiration lesions: layer of cortical tissue is drawn/peeled off

  2. Radio-frequency lesions: small lesions made by passing radiofrequency current through target tissue

  3. Knife cuts: cutting (sectioning) a nerve or tract

  4. Reversible lesions: e.g., by cooling or injecting an anesthetic

  5. Selective chemical lesions: injection of neurotoxins (neural poisons)

• Caution: Lesion effects are very difficult to interpret – you cannot destroy a structure without damaging neighbouring structures.

• Note: These are invasive methods used in animal research, not in humans.

What is neuropsychological testing? What are common tests and what do they measure?

• Idea: Standardised situation for all patients; focus is on the patient, not the researcher → allows objective comparison of data

• Applications:

  • School (learning problems, disabilities)

  • Clinical settings (e.g., depression)

  • Medical rehabilitation (stroke, accidents)

  • Medical-psychological investigation (e.g., German MPU / "Idiotentest")

• Common tests:

  • Wechsler Adult Intelligence Scale (WAIS): verbal comprehension, working memory, perceptual organization, processing speed

  • Tower of London (ToL): executive processing, planning

  • Beck Depression Inventory (BDI): 21 items, rating 0–3, sum score → severity of depression

  • Rey-Osterrieth Complex Figure Test: visuospatial abilities & visual memory (copy, immediate recall, delayed recall; scoring 0–2 per unit, max 36)

• Key point: Neuropsychological tests assess cognitive functions (memory, language, executive functions, etc.) in a standardised way.